The clinical manifestation of sepsis is often the consequence of cell interactions, resulting in excessive leukocyte activation and tissue injury. In spite of advances in the development of microbial antibiotics, biotechnology, and critical care management, morbidity and mortality due to sepsis related disorders has not significantly changed in the past 30 years. Clinically, the therapeutic options available to treat these disorders are limited, which reflects an insufficient understanding of the mechanisms that underlie these syndromes. Infectious agents and the subsequent host's response have been identified as major etiologic factors that contribute to the initiation and perpetuation of multiorgan injury. While clinical protocols have been developed to target the infectious aspect of these disorders, only experimental clinical trials have attempted to modify host-derived mediators. Studies directed at understanding the mechanisms which are responsible for the recruitment and activation of leukocytes during the evolution of acute systemic inflammation are the broad, long-term objectives of this application. The working hypothesis of this renewal application is the following: the participation of leukocytes during the evolution of experimental septicemia is mediated, in part, by the expression of murine MIP-2, a potent neutrophil chemotactic factor and a functional homologue of human IL-8, which is controlled by a balance of pro-inflammatory, early response cytokines and endogenous inhibitory mediators. Our investigations will focus on the following questions: l) What are the kinetics and cellular sources of MIP-2 during the evolution of acute systemic inflammation as it relates to TNF and IL-1? 2) What is the contribution of MIP-2 to the pathology of septicemia and organ injury? 3) What are the endogenous cytokine networks established between leukocytes and structural cells, which influence the expression of MIP-2? 4) What is the contribution of interleukin-l receptor antagonist (IRAP), soluble TNF receptors (sTNFr), and interleukin-10 (IL- 10) to the expression of MIP-2? and 5) What is the fate of MIP-2 mRNA using in vitro analyses? As an extension of the present studies, experimental endotoxemia and cecal ligation/puncture-induced septicemia will be utilized to assess the contribution of MIP-2 to evolving organ injury. Mechanisms for the expression and regulation of MIP-2 will be studied via interactions between early response cytokines IL-1 and TNF and their endogenous inhibitors, IRAP, sTNFr, and IL-10. Procedures used in our laboratory to address these questions include: bioassays, ELlSAs, immuno-histochemistry, Northern blot or RT-PCR, in situ hybridization, mRNA stability and nuclear run-on analyses. The studies designed in this proposal will demonstrate that MIP-2 plays a significant role in mediating the pathogenesis of multiorgan injury.